Rotary piston

ABSTRACT

In a rotating piston compressor plant for processing gas in conjunction with oil including an oil separator and an oil feedback line from the separator to the compressor, apparatus for simultaneously relieving the gas pressure on the oil separator and for blocking the feedback of oil to the compressor when the compressor is shut off, including a relief line for exhausting gas from the oil separator and a combination valve in the oil feedback line and the relief line actuated to an open position by the excess gas pressure on the pressure side of the compressor when operating and to a closed position by the excess gas pressure in the relief line when the compressor is shut off.

United States Patent 1191 Bauer Sept. 16, 1975 ROTARY PISTON 2,654,532 10/1953 Nichols 418/84 3,429,502 2 1969 L d 'k 4 [75] Inventor: Heinz Bauer, Munich, Germany M w 17/228 [73] Assignee: Bauer-Kompressoren, Hans Bauer, primary vrablik Mumch, Germany Attorney, Agent, or Firm-Millen, Raptes & White [22] Filed: Feb. 20, 1974 [211 App]. No.: 443,982 [57] ABSTRACT I In a rotating piston compressor plant for processing 30 F i Application Priority Data gas in conjunction with oil including an oil separator Feb 20 1973 German 2308265 and an oil feedback line from the separator to the i y compressor, apparatus for simultaneously relieving the [52] U S CI 4l8/84 Hg/8T 418/97, gaspressure on the oil separator and for blocking the 4l7/228 1 /625 feedback of oil to the compressor when the compres- [5 l 1 Int i 2 FOIC k sor is shut off, including a relief line for exhausting gas [58] 418/84 87 97400, from the oil separator and a combination valve in the 62/84 d oil feedback line and the relief line actuated to an open position by the excess gas pressure on the pres- 86] References Cited sure side of the compressor when operating and to a closed position by the excess gas pressure in the relief UNITED STATES PATENTS line when the compressor is shut off. 2,3()l ,034 1 H1942 Freeman et a] 417/228 2,384,293 9/1945 Freeman 418/84 9 Claims, 3 Drawing Figures PATENTEU SEP'! 6 i975 SHEET 1 [IF 3 ROTARY PISTON This invention relates to a rotating piston eompresor system with respectively one valve disposed in the gas conduit between the oil separator and the compressor and consumer, respectively, which valve is closed when the compressor drive is shut off, as well as to arrangements for the simultaneous relief of the oil separator and blockage of the oil feed to the operating chamber of the compressor. 1

Screw compressors are utilized, for example, in many cases for the compression of gaseous media. These devices are safe in operation and have quiet running characteristics. The'gaseous medium to be compressed is taken in through a suction nipple and compressed conventionally in the operating chamber of the compressor by being urged progressively through respectively two interlocking screw threads of two rotors arranged in a housing from the suction side to the high-pressure side of the compressor, wherein the volume of the thread cavities containing the gas or the air is respectively reduced. The thus-compressed gaseous medium is supplied to the consumer after exiting from the highpressure side of the compressor via a pressure line.

During the compression step, a fluid, normally oil, is utilized for cooling, lubricating. and sealing purposes, except in case of dry-operating compressors. The oil is customarily fed into the compressor operating chamber at the beginning of the compression procedure. After termination of the compression, the oil must again be separated from the compressed gas. For this purpose, an oil separator is arranged in the pressure line between the compressor and the consumer, In thisoil separator, the oil contained in the compressed gaseous medium is separated from the gas. The thus-separated oil is fed continuously back into the operating chamber of the compressor via an oil conduit, after passing through an oil cooler, as well as an oil filter.

If the compressor drive is shut off manually or by means of a pressure-responsive control valve located in the consumerline, care must be taken that the compressed gas, having beenfrecd of the oil, cannot pass again through the oil separator and from there through the compressor and'the suction nipple thereof out of the screw compressor plant andvbe expanded during this step. Therefore, a valve, normally a check valve, is provided in the consumer line which is closed when the compressor drive is shut off. and the gas pressure in the consumer line has thus dropped below a required value. Furthermore, the pressure line between the pressure nipple of the compressor and the inner space of the oil separator contains a further valve which is closed when the pressure in this pressure line drops below .a predetermined required value; this valve can the check valve and the oil separator, in order to relieve the load on the latter; a solenoid valve is arranged in this relief line which opens when'the compressor drive is shut off. Correspondingly, for the simultaneous blocking of the oil feed to the compressor operating chamber, a solenoid valve has been provided in the oil conduit coming from the oil separator shortly before the entrance of the oil conduit into the compressor; this solenoid valve is closed when the compressor drive is shutoff. However, the arrangement of the two solenoid valves has considerable disadvantages. Apart from the fact that the electrical part of these control valves means additional expenditure, solenoid valves donot have sufficient operating safety for the present application in compressors. In particular, the coils of these magnets can burn through or can be damaged in some other way, whereby the solenoid valves become inoperative; this can have very disadvantageous consequences for the entire screw compressor plant; For example, in such a case, the pressurized oil in the oil separator would suddenly flow unhindered into the operating chamber and from there through the suction nipple, which, in case of an open suction nipple (air compressor), would result in a strong contamination of the environment, not considering the associated losses in energy and oil. In connection with the above-mentioned susceptibility to trouble inherent in solenoid valves and particularly the coils thereof, it is to be pointed out in particular that compressors, and to a special extent. portable compressors, are frequently exposed to strong shocks and similar stresses.

In order to counteract these disadvantages encountered in solenoid valves, the two solenoid valves have been replaced in each case by a pneumatically con trolled valve. However, the expenditure in structural parts and energy connected with such valves and their control is likewise especially high. This holds true, in particular, with respect tothe requirement that the relief valve for the oil separator and the shutoff valve for the oil must be activated simultaneously when the comp'ressor is turned off,

The present invention is based on the problem of pro viding a rotating piston compressor system with respectively one valve disposed in the gas conduit between the oil separator and the compressor and consumer, respectively, which valve is closed when the compressor drive is shut off, as well as simple and particularly efficient arrangements for the simultaneous relief of the oil separator and blockage of the oil feed to the operating chamber of the compressor, wherein the arrangements for relieving the oil separator and for blocking the oil feed do not exhibit the disadvantages of the conventional devices.

also be suitably fashioned as a check valve. The lasti mentioned valve correspondingly serves the purpose of preventing, when the compressor drive has been turned off, the media present under pressure in the oil separator from flowing back through the pressure line, the operating chamber of the compressor, andthesuction nipple thereof.

However, on the other hand, steps must also be taken to effect, when the above valves, which are preferably fashioned as check valves, are closed, simultaneously a relieving of the oil separator and a blocking of the oil feed to the compressor operating chamber. It is known to connect a relief line to the consumer line between This problem is solved, in accordance with the present invention, by providing for the simultaneous relief of the oil separator and for blocking the oil feed to the compressor a single combination valve automatically controlled by the gas to be expanded from the oil separator and by the gas exiting from the compressor operating chamber on the pressure side.

The arrangement of this invention for the simultaneous relief of the oil separator and for blocking the oil supply to the compressor has very essential advantages as compared to the conventional systems in this field. The construction as a single, automatically controlled, combined valve represents an especially small expenditure in structural parts. A particularly important advantage resides in that the oil separator relief andthc oil blocking means, as well as the automatic control thereof, are combined'with each other and are accommodated in a single, compact valve body. Conse-. quently, the reliefof the oil separator and the blockage of the oil supply when the compressor drive is shut off take place with certainty absolutely synchronously, especially if these steps are automatically initiatedby one and the same valve stroke, advantageously.

' In accordance with a preferred embodiment, the combination valve has a piston member coaxially guided in a cylindrical housing element. this piston member being formed bytwo end-positioned drive pistons and two blocking pistons arranged between the drive pistons at a fixed mutual spacing and in coaxial relation to the drive pistons; one of the drive pistons is under the effect of the gas from the oil separator, which gas is to be expanded, and theother drive piston can be placed under the effect of the gas exiting on the pressure side from the operating chamber of the compressor, along the lines of mutually opposed axial directions of motion of the piston member. In this connection, the piston area which can be placed under the effect of the gas exiting from the operating chamber of the compressor on'the pressure side is larger than the piston area which can be placed under the effect of the gas to be expanded, which comes from the oil separator.

Advantageously, respectively one passageway disposed in the housing element is associated with the two blocking pistons; these two passageways are sealed off from each other.

The combination valve of the present invention has a simple structure. The valve is advantageously arranged in the proximity of the inlet of the oil conduit into the compressor, in view of the requirement, posed inter alia, that only a minimum amount of oil is to enter the interior of the compressor after the compressor drive has-been shut off. The oil conduit is connected on both sides to the oil passageway of the combination valve. Correspondingly, a relief line extends from the consumer line between the oil separator and the check valve to one end of the gas passageway and continues onthe other side of the gas passageway, where it is provided at its end advantageously with a noise damping means, through which the gas to be expanded can flowfrom the oil separator to the outside and/or into an expansion vessel. The fixedly joined blocking pistons, provided for the opening and closing, respectively, of the two passageways when the compressor drive is shut off, are each activated by an associated drive piston. Respeetively. one cylinder chamber is arranged in the housing element to place the two end-positioned drive pistons under pressure, one cylinder chamber being in communication with the relief line, while the other cylinder chamber is in communication with the pressure line between the pressure nipple of the compressor and the check valve, via a conduit. The piston area of the drive piston associated with this cylinder chamber which can be exposed to the pressure is preferably larger than the exposable piston area of the other drive piston.

During the operation of the compressor, the piston member of the combination valve of this invention, due to the load on the one, preferably larger, piston area exerted by the gas exiting on the pressure side from the operating chamber of the compressor and V passing through the aforementioned connection line into the associated cylinder chamber, is maintained in a position wherein the gas passageway of the combination valve is blocked by the associated blocking piston, whereas the oil passageway is open. However, when the compressor drive is turned off, the gas pressure drops in the pressure line and accordingly also in the cylinder chamber of the preferably larger drive piston. which chamber is in open communication with this pressure line. Consequently, the other drive piston, which is under the effect of the gas which is still essentially under compression final pressure. can urge the piston member into the opposite direction, so that presently the oil passageway is blocked by the associated blocking piston, whereas the gas passageway is open.

It is to be emphasized that the mode of operation of the combination valve according to the present invention is basically also safely ensured if the piston area chargeableby the gas exiting from the compressor operating chamber on the pressure side is no larger than the piston area exposed to the gas to be expanded, which comes from the oil separator. Due to the fact that the compressed gas, while passing through the oil separator, experiences a certain pressure loss as compared to the pressure value of the compressed gas prior to entering the oil separator, the pressure on the drive piston under the effect of the gas exiting from the compressor operating chamber on the pressure side is higher during the operation of the compressor than the pressure on the other drive piston which is under the effect of the gasto be expanded from the oil separator. Due to this pressure difference, the piston member of the combination valve of this invention is therefore always maintained in the position wherein the oil passageway is opened and the gas passageway is closed. even if the pistonareas of the two drive pistons which can be loaded are of the same size, during the operation of the compressor;

According to another advantageous embodiment, the combination valve of this invention comprises a piston member coaxially guidedin a cylindrical housing element, which piston member is formed by two drive pistons and a blocking piston arranged at a fixed distance between these drive pistons and coaxially with the latter. One drive piston, which has at its outer end a coaxial drive and blocking pin, can be under the load of the gas to be expanded, coming from the oil separator, and the other drive piston can be exposed to the gas exiting from the compressor operating chamber on the pressure side, along the lines of mutually opposed axial directions of motion of the piston member. The piston area chargeable by the gas exiting on the pressure side from the compressor operating chamber is preferably larger than the cross-sectional area of the drive and blocking pin which can be exposed to the gas to be expanded from the oil separator.

The surface area of the drive and blocking pin, serving for driving the piston member and for blocking the gas feed from the oil separator is advantageously of a conical configuration; a correspondingly beveled sealing edge is associated with this surface area, provided It is advantageous to associate with the blocking piston and with the drive and blocking pin of this embodi ment also respectively one passageway arranged in the housing element. these two passageways being mutually sealed.

The construction and mode of operation of this embodiment of the combination valve of the present inwntion basically correspond to the first-described embodiment. Because of the combined drive and blocking pin provided according to this invention. this lastdescribed embodiment of the combination valve exhibits still another simplification. For this feature makes it possible to utilize the passageway for the gas to be expanded. coming from the oil separator. simultaneously as the inlet conduit for this gas for the preceding drive of the drive and blocking pin. which is in the closed position. Additional explanations of the structural and functional details of this arrangement of the combination valve according to the present invention can be seen from the illustration in the drawings in conjunction with the description of a corresponding example.

The invention will be described hcreinbelow with ref erence to respectively one embodiment schematically illustrated in the drawings. to wit:

FIG. 1 shows a screw compressor plant with an arrangement according to this invention for the relief of the oil separator and for blocking the oil feed when the compressor drive is shut off;

FIG. 2 shows in detail a combination valve of the present invention as utilized in the arrangement of FIG. I. in an. axial longitudinal section; and

FIG. 3 shows in detail another embodiment of a combination valve according to this invention as utilized in the arrangement of FIG. I, in an axial longitudinal sec tion.

The screw compressor plant illustrated in FIG. 13, serving for example for the compression of air. has -a screw compressor 1. The operating chamber of the compressor 1 contains respectively one male rotor 2 and a female rotor 3 (not illustrated), these two rotors 2 and 3 meshing with each other. During the driving of the two rotors. indicated by the arrow 5 representing the rotation, by means of a drive system, not shown in the drawings. air is taken into the operating chamber of the compressor via the suction nipple 4. In the operating chamber. the air is compressed in the manner described hereinabove and then leaves the compressor through a pressure nipple 6 and a pressure line 7 joining the pressure nipple. in the direction toward the con sumer.

At the beginning of the compression step, oil is introduced into the operating chamber of the compressor for purposes of cooling. lubrication. and sealing; the oil must again be removed from the compressed air after the compression is terminated. For this purpose. the

pressure line 7 first enters an oil separator 8 wherein the compressed air and the oil are separated from each other in a conventional manner. The oil-free air leaves the oil separator 8 via a consumer line 9 in accordance with arrow 10 in the direction toward the consumer. Furthermore. the thus-separated oil flows from the oil chamber of the oil separator 8 continuously through an oil conduit 11 back into the compressor operating chamber 1 during the operation of the compressor. In the operating chamber, this oil is admixed to the air at the beginning of the compression. During its return. the oil is cooled by means of a cooler 12 and is then filtered through a filter 13. both components being arranged in the oil conduit 11.

Respectively one check valve 14 and 15 is inserted in the pressure line 7 and in the consumer line 9. The check valves 14 and 15 close automatically once the compressor drive is shut off manually or by means of a control system. not shown in the drawings. since during such step the pressure drops in the pressure line 7 and/or in the consumer line 9. This condition is shown in the drawing.

When the compressor drive is shut off. care must be taken simultaneously that the oil separator. sealed off by the two check valves 14 and 15, is relieved of pressure. and that furthermore any additional oil feed to the compressor 1 is blocked. For this purpose. a combination valve 16 of this invention is disposed in the proximity of the entrance of the oil conduit 11 into the operating chamber of the compressor 1, which valve is auto matically controlled by the gas to be expanded. coming from the oil separator 8, and by the gas exiting on the pressure side from the operating chamber of compressor l. The exact structure and mode of operation of the combination valve 16 will be described in detail below. referring additionally to the detailed illustration of the combination valve 16 in FIG. 2.

The combination valve 16 comprises a piston member 18 coaxially guided in a cylindrical housing element 17. The piston member 18 has two terminal-positioned drive pistons 19 and 20. as well as two blocking pistons 21 and 22., respectively. arranged between the drive pistons at a fixed mutual spacing and coaxially to the drive pistons. The drive piston 19 is under the effect of the gas to be expanded from the oil separator 8; this gas can flow unhindered into a cylinder chamber 25 associated with the drive piston 19 via a relief line 23 and a branching line 24. Correspondingly. the drive piston is charged by the gas exiting from the operating chamber of compressor 1.on the pressure side. which gas can flow unhindered into a cylinder chamber 27 associated with the drive piston 20 via a connection line 26. The cylinder chamber 27, in FIG. 2. has just been filled practically completely by the drive piston 20. In the embodiment shown in the drawing. which is preferred. the piston area 28 of the drive piston 20 which can be exposed to the gas is larger than the gas-chargeable piston area 29 of the drive piston 19 An oil passageway 30 is associated with the blocking piston 21. which passageway is arranged in the housing element 17 and is connected outside of the housing element 17 to the oil conduit 11. Correspondingly. a gas passageway 31 arranged in the housing element 17 is associated with the blocking piston 22, this gas passageway being connccted outside of the housing element 17 to the relief line 23. The two passageways 30 and 31 are sealed with respect to each other within the housing element 17 by means of a seal 32.

The drawings show the condition at the moment the compressor drive has been switched off. At this point in time. the pressure of the air exiting from the compressor l on the pressure side, which is also ambient in the connection line 26, drops to such an extent that the compressed air dammed up in the oil separator between the presently closed check valves 14 and 15 flows through the relief line 23 and the bypass line 24 into the cylinder chamber and maintains the drive piston 19 and, together therewith. the entire piston member 18, in the axial position illustrated in the draw- 21. Thus, no additional oil can pass any more to the opcrating chamber of the compressor 1. On the other hand, the blocking piston 22 is simultaneously in such an axial position that the gas passageway 31 is opened. Accordingly, the air to be expanded can flow from the interior of the oil separator 8, through the relief line 23 and a noise damping means 33 arranged at the end of this line, to the outside according to arrow 34, whereby the oil separator 8 relieved. i

However, once the compressor drive is'turned on again, the air pressure in the pressure nipple 6 of the compressor 1 and thus also in the connection line 26 leading to the cylinder chamber 27 and to the larger chargeable piston area 28 of the combination valve 16 is higher after a short period of time than the air pressure at the exit of the oil separator 8 and correspondingly in the relief line 23 and bypass line 24 leading to the cylinder chamber 25. At this point in time, the entire piston member 18 is urged in the direction of arrow 35 by the higher pressure effective on the drive piston 20 until, for example, the corresponding end face of the blocking piston 21 abuts a stop edge 36 of the housing element 17. in this position, the gas passageway 31 is then blocked by the blocking piston 22, while the oil passageway 30 is opened. The compressor unit in accordance with this invention can then operate appropriately; oil can continuously pass from the oil space of the oil separator 8 into the operating chamber of compressor 1 and. furthermore, there is no unnecessary efflux of compressed air from the compressor unit.

FIG. 3 shows in detail a combination \alve 16' modified according to this invention as compared to the combination valve 16. The combination valve 16' can be utilized in place of the combination valve 16 in a screw compressor plant according to FIG. 1. This modified combination valve corresponds with respect to its structure and mode of operation basically to the combination valve 16, but contains, in particular. an additional simplification as compared to the firstmentioned valve.

The combination valve 16' has a piston member 18' coaxially guided in a cylindrical housing element 17; this piston member 18 is formed by two drive pistons 19', 20 and a bb cking pin disposed therebetween at a fixed spacing and coaxially therewith. The drive piston 19, provided at its outer end with a coaxial drive and blocking pin 37, can be exposed (according to arrow 23') to the gas to be expanded, stemming from the oil separator 8; and the other drive piston 20 (arrow 26) can be affected by the gas exiting from the operating chamber of the screw compressor 1 on the pressure side, along the lines of mutually opposite axial directions of motion of the piston member 18". Also in this embodiment, the piston area 28, exposable to the gas exiting on the pressure side from the operating chamber of the screw compressor 1, is preferably larger than the cross-sectional area of the drive and blocking pin 37, which can be placed under the effect of the gas to be expanded, (D ming from the oil separator 8.

An oil passageway 30 is associated with the blocking piston 21 in the housing element 17'', the oil conduit 11 joining this passageway outside of the housing element 17'. Correspondingly, a gas passageway 31' arranged in the housing element 17', 39 is associated with the drive piston 19' and, in particular, with its-drive and blocking pin 37; the relicfline 23 joins this gas passageway outside of the housing element l7",-39. The two passageways 30' and 31 are mutually'scaled off within the housing element 17 by means'ofia seal 32".

1n the drawing, the condition is illustrated at the moment the compressor drive is being shut off, wherein the oil passageway 30 is blocked by the blocking piston 21'. On the other hand, the drive and blocking pin 37 is simultaneously in such an axial position that the gas passageway 31' is' opened. To ensure that the piston member 'l8'-eertainly reaches this axial position after the gas to be expanded from oil separator 8 has initially been effective on the drive and blocking pin 37, a compression spring 41 'coaxially surrounding the drive and blocking pin 37 is-arranged between the end wall 39 of the housing element 17 and the drive piston 19.

Once the compressor drive has been turned on again, the piston member 18' is urged, by the higher pressure from the compressor pressure nipple 6 effective on the drive piston 20, in the direction of arrow 35 until the conical end face 38 of the drive and blocking pin 37 is in firm contact with the associated, correspondingly beveled sealing edge 40 in the end wall 39. During this displacement step, the relatively minor spring force of the spring 41 is overcome.

As' indicated above, the combination valve 16' differs from the combination valve 16 essentially by the combined drive and blocking pin 37 arranged at the drive piston 19'.'Sinc"e the driving and blocking pin 37 serves for driving the piston member 18' by the gas to be expanded, stemming from the oil separator 8, as well as for blocking the passageway 31 for this gas by the combination'valve 16", the' gas passageway 31' forms, in a simple manner, simultaneously the inlet path for the gas from the oil separator 8 for charging the drive piston 19' and, in particular, the drive and blocking pin 37 thereof. Consequently, the'branching line 24 (FIG. 1) is omitted from this embodiment. The arrangement according to this invention for simultaneously relieving the oil separator and blocking the oil feedto the compressor when the compressor drive is shut off can be installed not only in newly manufactured rotating piston compressor plants, but also subsequently, with simple means, in corresponding, already used'plants, and even rather old plants.

What is-claimed is: y

1. In a rotating piston compressor plant utilizing an oil separator in a gas conduit between the pressure side of a compressor and a consumer output and an oil feedback line between the oil separator and the compressor, and having a first check valvein the gas conduit line between the compressor and the oil separator and a second check valve between the oil separator and the consumer output, said check valves being closed when the compressor is shut off, an apparatus for simultaneously relieving the gas pressure on the oil separator and for blocking the feedback of oil to the compressor when the compressor is shut off comprising:

a relief line for exhausting gas from said oil separator.

a combination valve in said feedback line and in said relief line havinganopen position forpermitting feedback of oil to said compressor and for blocking said relief line and a closed position for blocking said feedback line and opening said relief line. and means for automatically actuating said valve to the open position by expandinggas from the pressure side of said compressor when said compressor is on and for actuating said valve to the closed position at least by expanding gas from said oil separator when said compressor is shut off.

2. The apparatus of claim 1 wherein said combination valve comprises:

a cylindrical housing element.

a piston member coaxially guided in said cylindrical housing element, said piston member including two end positioned drive pistons and two blocking pis tons spaced between said drive pistons and coaxial therewith, forming a compressor gas pressure cylinder and an oil separator gas pressure cylinder, said piston member being reciprocable as a unit in said housing element.

3. The apparatus of claim 2 wherein said combination valve also includes:

individual passage ways for flow of said feedback oil and for flow of said gas exhausted from said oil separator, said passage ways being alternately blocked and opened by said blocking pistons by the reciprocation of said piston member, and

means sealing off said individual passage ways from each other.

4. The apparatus of claim 3 wherein the volume of said compressor gas pressure cylinder is larger than the volume of said oil separator gas pressure cylinder.

5. The apparatus according to claim 1 wherein said combination valve comprises:

a cylindrical housing element.

a piston member coaxially guided in said cylindrical housing element. said piston member including two drive pistons and a oil feedback blocking piston spaced between said drive pistons and coaxial therewith, forming a compressor gas pressure cylinder and an oil separator gas pressure cylinder,

said piston member being reciprocable as a unit in said housing element. and wherein said piston member also includes an integral drive and blocking pin in said oil separator gas cylinder, and wherein said means for automatically actuating said valve to the closed position at least by expanding gas from said oil separator includes a connection between said relief line and said oil separator gas pressure cylinder and wherein said pin blocks said connection when said valve is in said open position.

6. The apparatus according to claim 5 wherein said drive and blocking pin is conical in shape and wherein the surface of said connection blocked by said pin is of complementary contour.

7. The apparatus according to claim 6 wherein said combination valve also includes an individual passage way for flow of said feedback oil said passage way being alternately blocked and opened by said blocking piston by the reciprocation of said piston member and wherein said oil separation gas pressure cylinder includes an opening for exhaust of said expanding gas from said oil separator. and wherein said passage way is sealed off from said oil separation gas pressure cylinder.

8. The apparatus of claim 7 wherein said means for automatically actuating said valve to the closed position at least by expanding gas from said oil separator when said compressor is shut off also includes a compression spring in said oil separation gas pressure cylinder.

9. The apparatus of claim 7 wherein the volume of said compressor gas pressure cylinder is larger than the volume of said oil separation gas pressure cylinder. 

1. In a rotating piston compressor plant utilizing an oil separator in a gas conduit between the pressure side of a compressor and a consumer output and an oil feedback line between the oil separator and the compressor, and having a first check valve in the gas conduit line between the compressor and the oil separator and a second check valve between the oil separator and the consumer output, said check valves being closed when the compressor is shut off, an apparatus for simultaneously relieving the gas pressure on the oil separator and for blocking the feedback of oil to the compressor when the compressor is shut off comprising: a relief line for exhausting gas from said oil separator, a combination valve in said feedback line and in said relief line having an open position for permitting feedback of oil to said compressor and for blocking said relief line and a closed position for blocking said feedback line and opening said relief line, and means for automatically actuating said valve to the open position by expanding gas from the pressure side of said compressor when said compressor is on and for actuating said valve to the closed position at least by expanding gas from said oil separator when said compressor is shut off.
 2. The apparatus of claim 1 wherein said combination valve comprises: a cylindrical housing element, a piston member coaxially guided in said cylindrical housing element, said piston member including two end positioned drive pistons and two blocking pistons spaced between said drive pistons and coaxial therewith, forming a compressor gas pressure cylinder and an oil separator gas pressure cylinder, said piston member being reciprocable as a unit in said housing element.
 3. The apparatus of claim 2 wherein said combination valve also includes: individual passage ways for flow of said feedback oil and for flow of said gas exhausted from said oil separator, said passage ways being alternately blocked and opened by said blocking pistons by the reciprocation of said piston member, and means sealing off said individual passage ways from each other.
 4. The apparatus of claim 3 wherein the volume of said compressor gas pressure cylinder is larger than the volume of said oil separator gas pressure cylinder.
 5. The apparatus according to claim 1 wherein said combination valve comprises: a cylindrical housing element, a piston member coaxially guided in said cylindrical housing element, said piston member including two drive pistons and a oil feedback blocking piston spaced between said drive pistons and coaxial therewith, forming a compressor gas pressure cylinder and an oil separator gas pressure cylinder, said piston member being reciprocable as a unit in said housing element, and wherein said piston member also includes an integral drive and blocking pin in said oil separator gas cylinder, and wherein said means for automatically actuating said valve to the closed position at least by expanding gas from said oil separator includes a connection between said relief line and said oil separator gas pressure cylinder and wherein said pin blocks said connection when said valve is in said open position.
 6. The apparatus according to claim 5 wherein said drive and blocking pin is conical in shape and wherein the surface of said connection blocked by said pin is of complementary contour.
 7. The apparatus according to claim 6 wherein said combination valve also includes an individual passage way for flow of said feedback oil said passage way being alternately blocked and opened by said blocking piston by the reciprocation of said piston member and wherein said oil separation gas pressure cylinder includes an opening for exhaust of said expanding gas from said oil separator, and wherein said passage way is sealed off from said oil separation gas pressure cylinder.
 8. The apparatus of claim 7 wherein said means for automatically actuating said valve to the closed position at least by expanding gas from said oil separator when said compressor is shut off also includes a compression spring in said oil separation gas pressure cylinder.
 9. The apparatus of claim 7 wherein the volume of said compressor gas pressure cylinder is larger than the volume of said oil separation gas pressure cylinder. 